The present invention relates to a device for positioning a member so that it faces each of the perforations of a perforated plate, in accordance with a given grid. More specifically the invention relates to a device making it possible to position a guide tube in such a way that it faces each of the tubes of a steam generator, such as those equipping nuclear power stations, in order to successively introduce into each of the said tubes a control device, such as an eddy current probe or sensor.
It is known that the tubes of steam generators used in nuclear power stations are exposed to particularly severe operating conditions making it necessary to periodically inspect these tubes in such a way that damaged tubes can be condemned by the sealing of each of their ends.
For this inspection to take place, it must be possible to introduce an automatic device into the water box or tank of the steam generator, said device being controlled from the outside. Thus, it is desirable to reduce to a maximum any human interventions, as a result of the highly contaminated and radioactive nature of such water tanks, and their small size. For the same reasons, the device must be as reliable as possible and must enable all the tubes to be inspected without any manual intervention being needed. Furthermore, for easily understandable economic reasons, the time necessary for the inspection of all the generator tubes must be as short as possible.
A positioning device is known, which comprises two perpendicular arms provided with members permitting their independent fastening into the ends of tubes and whereby they can move with respect to one another in three perpendicular directions, so that the guide tubes carried by the arms can be made to face all the steam generator tubes.
This device generally gives satisfactory results and makes it possible to carry out complete remote control in a relatively short time of all the steam generator tubes. However, as has been shown by the brief preceding description, it has the disadvantage of having to be equipped with several guide tubes in order to permit a complete scan or sweep of the tube plate. This means that the equipment enabling the introduction of the eddy current sensor has to be disconnected from one and connected to another of the guide tubes when the area to be reached makes this necessary. Thus, this operation involves manual intervention, which it would be desirable to eliminate for the reasons referred to hereinbefore. Moreover, in normal operation, each tube to be controlled necessitates the displacement of the complete device. This is obviously unsatisfactory, because it increases the inspection time. Finally, this prior art device necessitates a complete availability of the tubes for its attachment. In practice this is obviously not the case because certain tubes have already been sealed as a result of preceding inspections. Moreover, the operation of the aforementioned device is interfered with when the systems of perforations are not orthogonal.